Microwave energy has been used in the prior art for extraction such as Ganzler, Salgo and Valko in Journal of Chromatography; 371, 1986: 299-306. However, this method applies microwave energy to a small amount of material immersed in a strongly absorbing medium resulting in most of the energy heating the medium, and a smaller amount affecting the material directly. Only thermal effects similar to conventional methods are noticed in this prior art process.
U.S. Pat. No. 5,458,897 to Pare discloses a method of extraction of various substances from organic material by exposure to microwave energy. The organic material is surrounded by a medium relatively transparent to microwaves, so that microwave energy is preferentially absorbed by the microwave absorbing constituents of the organic material, causing differential heating of the material over the medium sufficient to disrupt the structure of the organic material releasing the desired substances. Volatile oils and other substances can be extracted according to this method without significant heating.
U.S. Pat. No. 5,377,426 to Pare discloses a method of generating volatiles from liquid or solid materials enhanced by exposure to microwave radiation in the absence of solvent. Microwave energy according to this prior art method is absorbed preferentially by the liquid or solid material over generated gaseous volatiles allowing substantially complete volatilization of the desired substances.
Microwave energy has been shown to successfully enhance the extraction of desired components more quickly and efficiently than prior art methods, with greater selectivity and less product degradation. These methods rely on the different capacity of various materials to absorb microwave energy based on its dielectric constant. However, to date control of the microwave energy directed at the samples has been relatively random. While energy levels and frequency are known variables, direction and management of the microwave energy at high energy density levels has not been explored. In the prior art methods, high energy absorption would have necessitated extremely high power levels to induce an effect. Such high levels were not possible or practical, and cautionary means have been used to prevent accidental high energy exposure.
While microwave extraction has been shown to be effective, there is a need to develop protocols for extraction and sample treatment employing microwave energy concentrating means such as wave-guides at controlled frequency and energy levels, in order to reach an energy of activation to induce an effect. A focused microwave applicator and wave-guide can be used to raise the energy level of certain substances sufficiently to cause structural change or generate chemical reactions, and to significantly enhance the effectiveness of prior art microwave-assisted processes.